This invention relates to a method and a device for injection, especially for use in ambulatory treatment. More specifically, the invention relates to a method and a device by means of which an injection solution of a substance is prepared immediately before the injection, or in the preparation of several doses, before the first injection.
Injection devices for use in ambulatory treatment where the medicament is present in a solution are previously known and have been widely used in, for example, insulin treatment of diabetes. Such devices are usually built such that the patient himself can easily assemble a cylinder ampoule for one or more doses, and injection needle and a dosing device in a suitable holder and thereafter give himself easily the required injection. In the device it is also easy to exchange used ampoules and needles for new ones. In an assembled state, such injection devices are often shaped like a fountain-pen and can be easily brought along by the patient.
Moreover, so-called dual-chamber or mixing containers or cylinder ampoules are also known for preparation of solutions of sensitive substances immediately before the injection. Such containers are divided into two chambers separated by a movable wall or piston. The sensitive medicament is present in the front chamber in a dry, usually freeze-dried state and the front end of the front chamber is sealed by a wall penetrable to an injection needle. The liquid intended to dissolve the sensitive substance before the injection is present in the rear chamber. The two chambers are separated by a front movable wall and the rear end of the rear chamber is sealed by means of a rear movable wall. Furthermore, in the container wall there is arranged a connecting passage which can connect the front and the rear chambers.
In a storage position before the injection, there is no communication between the front and the rear chambers. The inlet as well as the outlet of the connecting passage end in the front chamber.
When the container is to be readied for injection, the rear, movable wall in the rear chamber is moved forwards, and due to the incompressibility of the liquid, the front movable wall will then also be moved forwards until it reaches a position just opposite the connecting passage in the wall of the container. When the rear movable wall thereafter is moved further forwards, the liquid will be pressed through the overflow passage into the front chamber where it will be brought into contact with the medicament and dissolved. At the injection the two walls will act together as a piston and press the prepared injection solution out through a needle introduced through the front end wall in the front chamber.
In certain cases the medicament can be so sensitive that special measures must be taken to protect the substance against mechanical influence at the time of dissolution as well as in the further handling of the solution. This applies for example to freeze-dried growth hormones where even a simple shaking of the substance and the liquid can lead to a non-acceptable biochemical change. The preparation of the container for injection must then be made with the utmost carefulness.
It would be very desirable to have available an injection device that is as easy to bring along and handle as those previously known for simple cylinder ampoules in which the medicament is present in a liquid state as a solution, suspension or emulsion, at the same time as the advantages of mixing containers at injection of sensitive substances might be utilized. This object is now achieved by the present invention.